Method of detecting a leak in a vacuum interrupter located inside a housing containing pressurized gas

ABSTRACT

A method is disclosed for detecting a leak in any one of the vacuum interrupters of a vacuum-type circuit breaker that comprises a plurality of vacuum interrupters disposed within a housing filled with pressurized insulating gas. The method comprises: (a) opening the circuit breaker and effectively disconnecting the closing mechanism of the breaker from the operating rod of the breaker so as to effectively preclude the closing mechanism from exerting a closing force on the operating rod, (b) measuring the net force on the operating rod after (a) has been performed, and (c) comparing the measured net force to a standard value corresponding to the force on the operating rod when the interrupters are intact and the insulating gas is at the same pressure as when the net force was measured.

United States Patent I [191 Sofianek I June 4, 1974 METHOD OF DETECTING A LEAK IN A VACUUM INTERRUPTER LOCATED INSIDE A HOUSING CONTAINING PRESSURIZED GAS [75] Inventor: Joseph C. Sofianek, Broomall, Pa.

[73] Assignee: General Electric Company,

Philadelphia, Pa.

[22] Filed: July 11, 1973 1211 Appl. No.: 378,339

[52] US. Cl. 200/144 B [51] Int. Cl. Il0lh 33/66 {58] Field of Search 200/144 B [56] References Cited UNITED STATES PATENTS 3.404.247 10/1968 Glassands ZOO/144B 3.472.981 10/1969 McCarty et a]. 200/144 B 3.493.952 2/1970 .lette 200/144 B 3.626.125 12/1971 Tonegawa 200/144 B Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-William Freedman; J.

' Wesley Haubner [57] ABSTRACT A method is disclosed for detecting a leak in any one of the vacuum interrupters of a vacuum-type circuit breaker that comprises a plurality of vacuum interrupters disposed within a housing filled with pressurized insulating gas. The method comprises: (a) opening the circuit breaker and effectively disconnecting the closing mechanism of the breaker from the operating rod of the breaker so as to effectively preclude the closing mechanism from exerting a closing force on the operating rod, (b) measuring the net force on the operating rod after (a) has been performed. and (c) comparing the measured net force to a standard value corresponding to the force on the operating rod when the 'interrupters are intact and the insulating gas is at the same pressure as when the net force was measured.

3 Claims, 4 Drawing Figures PATENTEBJUN 41914 SHEEY 1 BF 2 PATENTEDJ N 4 m4 3,814,885

saw 2 BF 2 v430 0 E Q QJ.

. 1" I METHOD OF DETECTING A LEAK IN A VACUUM INTERRUITER LOCATED INSIDE'A HOUSING CONTAINING PRESSURIZ ED GAS BACKGROUND This invention relates to a method of detecting a leak in a vacuum interrupter that is located within a housing containing pressurized insulating gas and is especially applicable to a high voltage vacuum circuit breaker in which the vacuum interrupter is one of a plurality of series-connected interrupters located within the gasfilled housing of thecircuit breaker.

One way of checking a vacuum interrupter for a leak is to apply a high potential across its terminals. If the interrupter has a leak which has allowed the pressure therein to rise to a level of 0.01 torr or higher, then the high potential will ordinarily produce a sparkover within the interrupter which can be readily detected.

This known method of checking for loss of vacuum can readily beused with vacuum circuit breakers in which the individual interrupter terminals are accessible for application of the high potential thereto. The interrupters of such a circuit breaker can be tested by applying the high potential across the terminals of each interrupter. But in certain vacuum circuit breakers, e.g., high voltage circuit breakers which comprise set-- ies-connectedinterrupters stacked within a closed housing, the terminals of the interrupters may not be accessible unless the entire circuit breaker pole is dismantled.

SUMMARY Accordingly, an object of my invention is to provide a method of detecting a leak in an individual vacuum interrupter of such a circuit breaker which does not require dismantling of a large portion of the circuit breaker even though the terminals of the individual interrupters are not readily accessible without such dismantling.

Another object is to provide a leak-detecting method that fulfills the immediatelypreceding object and is also usable with a circuit breaker in which the interrupters are disposed within a pressurized insulating gas. Such a gas can interfere with leak testing by means of a simple high-potential test because if the leak is large, the gas pressure within the interrupter will approach or even equal'that outside the interrupter. The resulting high dielectric strength within the interrupter can prevent any sparkover by the high-potential test voltage.

In carrying out my invention in one form, I provide a method for detecting a leak in any one of the interrupters of a vacuum-type circuit breaker comprising: (i) a housing filled with pressurized insulating gas, (ii) a plurality of vacuum interrupters located within said housing and in said pressurized gas, each interrupter comprising an evacuated envelope and a movable contact rod extending in sealed relationship through said envelope so that said pressurized gas biases each of said contact rods toward a contact-closed position with a force dependent upon the pressure of said gas, (iii) an operating rod extending into said housing from a point exterior to the housing, (iv) means for coupling said operating rod to said contact rods, (v) a seal around said operating rod where it enters said housing so that the gas within said housing exerts' on said operating rod'a force dependent upon the pressure of said gas tending to eject said operating rod from said housing, and (vi) a closing mechanism for supplying closing force to said operating rod to effect closing of the interrupters and circuit breaker. The method comprises: (a) opening the circuit breaker and effectively disconnecting the closing mechanism from the operating rod so as to effectively preclude the closing mechanism from exerting a closing force on the operating rod, (b) measuring the net force on the operating rod when the closing mechanism is effectively disconnected therefrom, and (c) comparing the measured net force to a standard value corresponding to the force on the operating rod when the interrupters are intact and the gas is at the same pressure as when the net force was measured.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction within the accompanying drawing, wherein:

FIG. 1 is a schematic showing of a high voltage vacuum circuit breaker to which my invention can be applied. The circuit breaker is shown in its closed posi- DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. I, the circuit breaker shown therein comprises a housing 10 defining an internal chamber 16 that is filled with pressurized insulating gas, such as, for example, sulphur hexafluoride at a pressure of about 50 p.s.i. gage. The illustrated housing comprises a tubular casing 12 of insulating material and end caps 13 and I4 sealed to the casing 12 at its opposite ends. The pressure of the gas within the chamber 16 is indicated by a suitable gauge 15.

Located withinthe chamber 16 of housing 10 are a plurality of series-connected vacuum interrupters 20. Each of these interrupters is of a conventional design and, as such, comprises a highly evacuated envelope 25 and a pair of separable contacts 26 and 27 located within the envelope 25. Envelope 25 comprises a tubular casing 21 of insulating material and end caps22 and 23 sealed to the casing at its opposite ends. The normal pressure within envelope 25 is about 10" torr or lower. The upper contact 26 is a stationary contact mounted on a stationary contact rod 28 extending in sealed relationship through the top end cap 22 of interrupter envelope 25. The lower contact is a movable contact fixed to a movable contact rod 30 extending freely through the lower end cap 23 of interrupter envelope 25. A flexible metal bellows 32, which is joined at its opposite ends to rod 30 and end cap 23, provides a vacuum-tight seal about rod 30 that allows the rod to be moved vertically without impairing the vacuum inside-the envelope.

In the illustrated embodiment, each interrupter 20 is mounted on a bracket 35 that is, in turn, suitably secured to the circuit breaker housing 10. Preferably, the

. contact rod 28 of the uppermost interrupter 20 has an extension that extends in sealed relationship through the upper end cap 13 and is suitably electrically connected thereto. The interrupters 20 are electrically connected in series between the terminals 13 and 14 by suitable flexible conductors shown schematically at 37.

bars 43 interconnect the tie rods 42 in spaced locations adjacent the bottoms of the respective interrupter housings. The movable contact rod 30 of each interrupter is connected to its associated cross bar 43 through a wipe device 55 of a conventional design, soon to be described in more detail. Suitable guides (not shown) are provided within the circuit breaker housing for guiding the linkage 42, 43 for straight line movement in a vertical direction. 8

One of the wipe devices 55 is shown in more detail in FIG. 3 in a circuit breaker-closed position. As will be apparent from FIG. 3, this wipe device comprises a cylindrical driving part 56 coupled through a rod 56a to the cross bar 43 and a piston-like driven part 57 coupled to the contact rod 30. A compression spring 58 urges driven part 57 upwardly toward engagement with an annular stop 59 on the cylindrical driving part 56. When driving part 56 is driven in a downward opening direction from its position of FIG. 3, a limited amount of initial downward movement of part 56 occurs independently of piston 57, after which stop 59 strikes piston 57 and carries the contact rod 30 through its downward opening stroke. When the circuit breaker is in its open position, the parts of the wipe device 55 occupy the positions depicted in FIG. 4.

The lower cross bar 43 (FIGS. 1 and 2) is connected to a vertically-extending operating rod 45 that extends freely through the lower end cap 14 of the circuit breaker housing 10. A seal in the form of a flexible bellows 47 surrounds the operating rod 45. This bellows is joined at its upper end to the end cap 14 and at its lower end to the operating rod 45. It will be apparent that the pressurized gas within housing exerts a force on the operating rod 45 tending to eject the operating rod from the housing 10. This force is directly dependent upon the gas pressure within the circuit breaker housing 10 and the effective area of the seal 47.

Opening of the circuit breaker is effected by driving the operating rod downwardly, thus driving the linkage 42, 43 and the movable contact rods 30 of the interrupters downwardly so as to produce separationof the contacts 26, 27 of all the interrupters. The force for driving operating rod 45 downwardly through its opening stroke is derived from an opening spring 50 shown at the bottom of the circuit breaker housing 10. Spring 50 is a compression spring, the upper end of which bears on the end plate 14 and the lower end of which bears against a thrust plate 52, which in turn bears against a shoulder 54 on the operating rod 45. When the circuit breaker is in its closed position, as shown in FIG. 1, a latch 60 holds the operating rod 45 in its elevated position, thus maintaining opening spring 50 compressed. When latch 60 is released, opening spring 50 is free to expand and drive operating rod 45 downwardly through an opening stroke into the position of FIG. 2. The opening stroke is terminated when a shoulder 61 fixed to operating rod 45 strikes a suitable buffer 62, as shown in FIG. 2.

Closing of the circuit breaker is effected by driving the operating rod 45 upwardly through a closing stroke from its position of FIG. 2 into its position of FIG. 1. This drives the linkage 42, 43 upwardly, carrying contact rods through an upward closing stroke. The wipe devices 55 allow the linkage 42, 43 to continue upwardly through a small amount of overtravel, or wipe, after the contacts 27, 26 engage. The force for driving the operating rod through its closing stroke is derived from a suitable closing mechanism 65 (FIG. 1).

When it is desired to check the interrupters 20 for leakage, the circuit breaker is operated to its open position of FIG. 2, if it is not already open, and it is electrically disconnected from its power circuit by opening suitable disconnect switches (not shown). Then, the closing mechanism 65 is disconnected from the operating rod 45 so that the closing mechanism exerts no effective force on the operating rod. Such mechanism disconnection can be effected by removing a connecting pin 67 from the coupling 69 that interconnects the operating rod and the closing mechanism. Next, the opening spring 50 is effectively disconnected from the operating rod 45 by operating a plurality of jack screws (such as shown at 68 in FIGS. 1 and 2) in a direction to drive the thrust plate 52 upwardly out of engagement with shoulder 54. When the jack screws have been thus operated, all force developed by the compression spring 50 is transmitted through the jack screws to the stationary housing 70 for the spring and none is transmitted to the operating rod 45.

The next step in the leak test is to measure the net vertically-acting force on the operating rod. The magnitude of this force is indicative of whether a leak is present in any of the interrupters. In this respect, note that pressurized gas within circuit breaker housing 10 acting on the contact rod and bellows 32 of each vacuum interrupter exerts an upward force on the contact rod, assuming that the interrupter is in its normal lowpressure condition. The total upward force is the sum of the upward forces thus developed at the four interrupters. Opposing this upward force is the weight of the linkage 42, 43 and operating rod 45 plus the downward force that the pressurized gas exerts on the operating rod 45 at the seal 47, as described hereinabove. The net force on the operating rod is the sum of these upward and downard components, considering the forces in one direction as positive and those in the opposite direction as negative. For any value of gas pressure within the circuit breaker housing 10 (assuming the opening means 50 and the closing means 65 are effectively disconnected), there will be a predetermined standard value of net force acting vertically on the operating rod if the interrupters are intact, i.e., in their normal low-pressure condition. By observing the pressure in the housing 10 on gauge 15 and determining whether the measured value of net force equals the predetermined standard value for this particular gas pressure, the technician can determine whether there is a major leak in anyone of the interrupters. If the measured net force differs substantially from the standard value, a leak is indicated.

Although I prefer to effectively disconnect the opening springfrom the operating rod 45, as above described, prior to measuring the force on the operating rod, my invention in its broader aspects can be practiced without this step. In this regard, the force that the opening spring normally exerts when the circuit breaker is open can be determined beforehand, and the technician can deduct this value of force from the net force measured on the operating rod. This approach,

I however, does not allow for variations in spring force,

and thus a more accurate and reliable procedure is the above-described one of effectively disconnecting the opening spring prior to making the force measurement.

It is to be noted that the above-described forcemeasuring test is performed on the circuit breaker when it is in its open position. This is advantageous because when the circuit breaker is in this position, its operating rod can be more fully isolated from the forces (other than gas pressure) which otherwise act on it. In this connection, note that the wipe springs 58 in the various wipe devices 55 are exerting no net force on the operating rod when the circuit breaker is open, as will be apparent from FIG. 4.v

The force-measuring test described in the three immediately-preceding paragraphs, while providing agood indication of a major leak in an interrupter, is not sufficiently sensitive to reliably indicate whether a minor leak is present. If the-leak is one which merely raises the pressure into the range of approximately 0.01

to 50 torr, there will not be a significant change in net force on the operating rod 45. To test for this type of leak, l'apply a moderate voltage across the terminals of the circuit breaker. If the pressure inside any one of the interrupters isin the above range, is applied voltage will produce a glow discharge within the leaking interrupter. Since the interrupter casing 21 is transparent, or at least translucent, the glow from the discharge will appear in the chamber 16 within circuit breaker housing 10. A light-sensitive device 75 within the chamber 16 senses this flow and develops a signal indicative of the presence of the glow, thus providing an indication of whether a minor leak has occurred in one of the interrupters.

This electrical test is not sufficient as a test for a major leak because such a leak can result in the interrupters filling with gas of a pressure approaching or even equaling that in chamber 16. This gas has a high dielectric strength, and there is thus a significant chance that the applied voltage would produce no sparkover or glow within the interrupter. The abovedescribed force-measuring test is therefore used to check for a major leak.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications maybe made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my inventron.

What i claim as new and desire to secure by Letters Patent of the United States is:

1. For use with a vacuum-type circuit breaker comprising: (i) a housing filled with pressurized insulating gas, (ii) a plurality of vacuum interrupters located within said housing and in said pressurized gas, each interrupter comprising an evacuated envelope and a movable contact rod extending in sealed relationship through said envelope so that said pressurized gas biases each of said contact rods toward a'contact-closed position with a force dependent upon the pressure of said gas, (iii) an operating rod extending into said housing from a point exterior to the housing, (iv) means for coupling said operating rod to said contact rods, (v) a seal around said operating rod where it enters said housing so'that the gas within said housing exerts on said operating rod a force dependent upon the pressure of said gas tending to eject said operating rod from said housing, and (vi) a closing mechanism for supplying closing force to said operating rod to effect closing of said interrupters and circuit breaker; a method of detecting a leak in one of said interrupters comprising:

a. opening said circuit breaker and effectively disconnecting said closing mechanism from said operating rod so as to effectively preclude said closing mechanism from exerting a closing force on said operating rod,

b. measuring the net force on said operating rod when said closing mechanism is effectively disconnected therefrom,

c. comparing said net force to a standard value corresponding to the force on said operating rod when said closing means is effectively disconnected therefrom, said interrupters are intact, and the gas is at a pressure equal to that prevailing at the time said net force is measured.

2. The method of claim 1 in combination with the additional steps of:

a. applying voltage across said plurality of vacuum interrupters, and

b. detecting the presence within said housing of any glow emitted from an electrically stressed interrupter that has lost some but not all of its vacuum.

an interrupter leak to be more accurately measured. 

1. For use with a vacuum-type circuit breaker comprising: (i) a housing filled with pressurized insulating gas, (ii) a plurality of vacuum interrupters located within said housing and in said pressurized gas, each interrupter comprising an evacuated envelope and a movable contact rod extending in sealed relationship through said envelope so that said pressurized gas biases each of said contact rods toward a contact-closed position with a force dependent upon the pressure of said gas, (iii) an operating rod extending into said housing from a point exterior to the housing, (iv) means for coupling said operating rod to said contact rods, (v) a seal around said operating rod where it enters said housing so that the gas within said housing exerts on said operating rod a force dependent upon the pressure of said gas tending to eject said operating rod from said housing, and (vi) a closing mechanism for supplying closing force to said operating rod to effect closing of said interrupters and circuit breaker; a method of detecting a leak in one of said interrupters comprising: a. opening said circuit breaker and effectively disconnecting said closing mechanism from said operating rod so as to effectively preclude said closing mechanism from exerting a closing force on said operating rod, b. measuring the net force on said operating rod when said closing mechanism is effectively disconnected therefrom, c. comparing said net force to a standard value corresponding to the force on said operating rod when said closing means is effectively disconnected therefrom, said interrupters are intact, and the gas is at a pressure equal to that prevailing at the time said net force is measured.
 2. The method of claim 1 in combination with the additional steps of: a. applying voltage across said plurality of vacuum interrupters, and b. detecting the presence within sAid housing of any glow emitted from an electrically-stressed interrupter that has lost some but not all of its vacuum.
 3. The method of claim 1, as used with a vacuum circuit breaker that includes opening spring means acting on said operating rod and biasing said interrupters toward open position, which method comprises performing before (b) of claim 1 the additional step of: effectively disconnecting said opening spring means from said operating rod so that said opening spring means no longer exerts an opening bias on said operating rod, thus enabling variations in said net force attributable to an interrupter leak to be more accurately measured. 